Collapse of Mayan Civilization Traced to Dry Spells

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The collapse of the ancient Mayan civilization may have been
linked to relatively modest dry spells, researchers now say.

The
ancient Mayan empire once stretched across an area about the
size of Texas, with cities and fields occupying what is now
southern Mexico and northern Central America, including the
countries of Guatemala, Belize, El Salvador and Honduras. The
height of the Mayan empire, known as the Classic period, reached
from approximately A.D. 250 to at least A.D. 900.

The ancient Maya had what was arguably the most advanced
civilization in the Americas. For instance, they made dramatic
breakthroughs in astronomy that helped them very accurately
predict where the moon and other planets would be in the sky
centuries in the future. They also left behind many books and
stone inscriptions regarding the
stories of their gods and the history of their divine kings
and queens.

For unknown reasons, the ancient Mayan civilization then
disintegrated more than a millennium ago. The number of people
declined catastrophically to a fraction of the empire's former
size, and the ruins of its great cities are now largely overgrown
by jungle. [ Photos:
First Glimpse into a Mayan Tomb ]

Scientists have long drawn connections between
the slow decline of the ancient Maya, which took about two
centuries, "to climate change, and especially to drought," said
researcher Martín Medina-Elizalde at the Yucatan Center for
Scientific Research in Mexico. "No sound estimates had been made
about the severity of this drought, but some have suggested
extreme scenarios."

To see how much rainfall the ancient Maya saw before the demise
of their civilization, the researchers combined the four most
detailed records of past climate changes known regarding the
civilization's collapse — three from nearby lakes and one from a
stalagmite, a mineral formation that grows upward from a cave
floor. This helped develop a model of "the region's balance
between evaporation and rainfall," Medina-Elizalde said.

The scientists found that rainfall in the region decreased
episodically for periods as long as a decade at a time.

"Our results show rather modest rainfall reductions between times
when the Classic Maya civilization flourished and its collapse
between 800 to 950," said researcher Eelco Rohling, a
paleoclimatologist at the University of Southampton in England.
"These reductions amount to only 25 to 40 percent in annual
rainfall, but they were large enough for evaporation to become
dominant over rainfall, and open water availability was rapidly
reduced. The data suggest that the main cause was a decrease in
summer storm activity."

The timing of these dry spells might help explain why modest
reductions in rainfall still may have helped cause the demise of
a well-established civilization.

"Summer was the main season for cultivation and replenishment of
Maya freshwater storage systems and there are no rivers in the
Yucatan lowlands," Rohling said.

It appeared to Rohling that the ancient Maya had become reliant
on continuous rainfall supplies, and had stretched the capacity
of their farmlands to a fine limit based on normal levels of
rain. "Then, even a rather subtle climatic change was enough to
create serious problems," he told LiveScience. "Societal
disruptions and abandonment of cities are likely consequences of
critical water shortages, especially because there seems to
have been a rapid repetition of multiyear droughts."

Rohling emphasized they are not saying that climate ended the
ancient Mayan civilization. "We are documenting that there was a
reduction in rainfall, and that reservoirs of water were
evaporating," he said. This may in turn have led to societal
unrest or diseases or both, "which are more likely to explain the
actual collapse of society."

The scientists noted that the droughts they saw during the demise
of the ancient Mayan civilization were similar in severity to
those projected by the Intergovernmental Panel on Climate Change
(IPCC) for the near future in the same region. [ 10
Surprising Results of Global Warming ]

"There are differences too, but the warning is clear — what seems
like a minor reduction in water availability may lead to
important, long-lasting problems," Medina-Elizalde said. "This
problem is not unique to the Yucatan Peninsula, but applies to
all regions in similar settings where evaporation is high. Today,
we have the benefit of awareness, and we should act accordingly."

The scientists detailed their findings in the Feb. 24 issue of
the journal Science.

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